Multilayer optical films (MOFs) have been made by co-extrusion of polymers. The final film can include a large number of alternating polymer layers of high and low refractive index and can be referred to as a Bragg reflector, or a 1-D photonic crystal. Light can be selectively reflected or transmitted at different wavelengths based on constructive interference from light reflected at the layer stack interfaces. MOFs have been designed primarily to reflect IR and/or visible light. Common polymers utilized in MOF includes PEN, PMMA, co-PMMA, PET, co-PET and co-PEN.